//C17.18:append.cpp -- appending information to a file
#include <iostream>
#include <fstream>
#include <stdint.h>
#include <stdlib.h>
#include <string>
#include <cstdlib>    // (for exit())

const char * file = "guests.txt";
int main(void)
{
    using namespace std;
    char ch;
    // show initial contents
    ifstream fin;
    fin.open(file);

    if(fin.is_open())
    {
        cout << "Here are the current contents of the "
             << file << " file:\n";
        while(fin.get(ch))     
        {
            cout << ch;
        }
        fin.close();
    }
    // add new names
    ofstream fout(file, ios::out | ios::app);
    if(!fout.is_open())
    {
        cerr << "Can't open" << file << "file for output.\n";
        exit(EXIT_FAILURE);
    }

    cout << "Enter guest names (enter a blank line to quit):\n";
    string name;
    while(getline(cin,name) && name.size() > 0)
    {
        fout << name << endl;
    }
    fout.close();
    // show revised file
    fin.clear();    // not necessary for some compilers
    fin.open(file);
    if(fin.is_open())
    {
        cout << "Here are the new countents of the "
             << file << " file:\n";
        while(fin.get(ch))      
        {
            cout << ch;
        }
        fin.close();
    }
    cout << "Done.\n";
}
